TY  - INPR
A1  - Dicken, Volker
T1  - Simultaneous activity and attenuation reconstruction in emission tomography
N2  - In single photon emission computed tomography (SPECT) one is interested in reconstructing the activity distribution f of some radiopharmaceutical. The data gathered suffer from attenuation due to the tissue density µ. Each imaged slice incorporates noisy sample values of the nonlinear attenuated Radon transform (formular at this place in the original abstract) Traditional theory for SPECT reconstruction treats µ as a known parameter. In practical applications, however, µ is not known, but either crudely estimated, determined in costly additional measurements or plainly neglected. We demonstrate that an approximation of both f and µ from SPECT data alone is feasible, leading to quantitatively more accurate SPECT images. The result is based on nonlinear Tikhonov regularization techniques for parameter estimation problems in differential equations combined with Gauss-Newton-CG minimization.
T3  - NLD Preprints - 50 
KW  - SPECT
KW  - tomogrphy
KW  - attenuated Radon transform
KW  - nonlinear invers problem
KW  - Tikhonov regularization
KW  - nonlinear optimization
Y1  - 1998
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-14747
ER  - 
TY  - INPR
A1  - Böckmann, Christine
A1  - Niebsch, Jenny
T1  - Examination of the nonlinear LIDAR-operator : the influence of inhomogeneous absorbing spheres on the operator
N2  - The determination of the atmospheric aerosol size distribution is an inverse illposed problem. The shape and the material composition of the air-carried particles are two substantial model parameters. Present evaluation algorithms only used an approximation with spherical homogeneous particles. In this paper we propose a new numerically efficient recursive algorithm for inhomogeneous multilayered coated and absorbing particles. Numerical results of real existing particles show that the influence of the two parameters on the model is very important and therefore cannot be ignored.
T3  - NLD Preprints - 47 
KW  - multiwavelength lidar
KW  - aerosol size distribution
KW  - inverse ill-posed problem
KW  - multilayered coated and absorbing aerosol
KW  - new recursive algorithm
Y1  - 1998
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-14725
ER  -